The present invention relates generally to cascade voltage multiplier circuits of the Cockcroft-Walton type, but more particularly relates to the use of such circuits to develop high voltages in electrostatic spray guns.
The use of semiconductor diodes and capacitors in cascade voltage multiplier circuits to develop high voltage for electrostatic spraying operations is well known in the art. Such circuits have long been used to develop high voltages at a remote location, which high voltage is then conveyed to a spray gun by means of a suitable power cable, and is applied to an electrode associated with the spray gun for developing an electrostatic charging voltage to assist in the application of paints and other liquids. More recently, such circuits have been reduced in size sufficiently to become mounted directly in the spray gun body itself, to multiply the magnitude of a low voltage alterating current supplied to the multiplier to achieve a predetermined electrostatic potential.
Each of the stages of such a voltage multiplier is constructed from a well-known voltage doubler circuit design, and a plurality of such stages are cascaded to create relatively high electrostatic voltages, in the range of 50 to 150 kilovolts (kV). Voltages in this range are suitable for electrostatic charging of sprayed liquids.
One of the problems of utilizing such cascade voltage multiplier circuits in spray guns is caused by the relatively large physical size required to contain circuits capable of producing a reasonable electrostatic voltage. A significant number of cascaded stages are required, and the spray gun body enclosing such circuits must contain sufficient insulating material to eliminate the possibility of dielectric breakdown which would otherwise occur at high electrostatic voltages. Dielectric breakdown problems also require that individual circuit components within a cascade multiplier be physically spaced at reasonable distances in order to avoid inter-stage arcing within the multiplier.
The number of voltage multiplier stages required in order to develop sufficiently high voltage for effective use in electrostatic spraying presents a further problem in the design of spray guns. For example, it is not unusual to require 10-12 cascaded stages in order to develop the required voltage, and a voltage multiplier having this number of stages occupies a significant length dimension. If such a voltage multiplier is mounted directly in a spray gun body, it results in the spray gun body becoming large, unwieldy, and heavy. All of these factors are undesirable in connection with spray gun design, for it is always a design objective to create a lightweight spray gun which is easy to manipulate and comfortable to handle. Therefore, it is desirable to minimize the physical size of cascade voltage multiplier circuits when such circuits are incorporated directly into spray gun bodies.